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Full Discussion: Invalid back reference
Top Forums UNIX for Dummies Questions & Answers Invalid back reference Post 302724959 by alister on Thursday 1st of November 2012 01:34:01 PM
Old 11-01-2012
Quote:
Originally Posted by vaz0r
I tried using the following expression:
Code:
 egrep '.*\[.*>\(........\).*\].*\.>\1\.' file

Unfortunately I received the following error message: 'egrep: Invalid back reference'. Does anyone know what i am doing wrong? Or any suggestions how I could solve this problem?
For two reasons, just use grep, not egrep.

(1) Nothing about your regular expression requires using the extended flavor of regular expression. As a matter of fact, as it's written, it's using the basic flavor. The \( sequence creates a back reference in the basic flavor. In egrep's extended flavor that just matches a literal parenthesis.
(2) POSIX extended regular expressions do not support back references. Your code will probably work with GNU egrep extensions, but will fail with most other egrep. implementations.

Regards,
Alister

Last edited by alister; 11-01-2012 at 02:41 PM..
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iv_thread(3)						    ivykis programmer's manual						      iv_thread(3)

NAME
iv_thread_create, iv_thread_set_debug_state - ivykis thread convenience functions SYNOPSIS
#include <iv_thread.h> int iv_thread_create(char *name, void (*start_routine)(void *), void *arg); void iv_thread_set_debug_state(int state); DESCRIPTION
iv_thread_create is a wrapper around pthread_create(3) which will maintain an ivykis main loop reference in the calling thread (which must be an ivykis(3) thread, i.e. have had iv_init(3) called in it) for as long as the created thread is alive. Maintaining a reference on the calling thread's ivykis event loop makes sure that the calling thread will not return from its ivykis main loop before the created thread exits, as that could cause cleanup still happening in the created thread to be interrupted when the calling thread subsequently calls exit(3). The created thread need not be an ivykis thread. Enabling debugging by calling iv_thread_set_debug with a nonzero argument will print a debug message to standard error whenever a thread is created via iv_thread_create, whenever a thread so created terminates normally by returning from its start_routine, self-terminates by calling pthread_exit(3), or is successfully canceled by pthread_cancel(3), and whenever destruction of such a thread is signaled back to the calling thread. For inter-thread signaling, iv_thread uses iv_event(3). SEE ALSO
ivykis(3), iv_event(3), exit(3), pthread_cancel(3), pthread_create(3), pthread_exit(3) ivykis 2010-09-13 iv_thread(3)
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